A typical computer network, such as an internet protocol (IP) network, supports communications between various network devices that may comprise personal computers, laptops, workstations, personal-digital assistants (PDAs), wireless devices, network-ready appliances, file servers, print servers, routers, or other devices. When two devices communicate, the devices establish a communication session using a communication protocol, such as the transmission control protocol (TCP). Devices, referred to as routers, forward packets associated with the communication session through the physical network that connects the devices. The flow of packets between the devices for a TCP session is commonly referred to as a TCP flow.
Various kinds of processing of the TCP flow can be done by intermediate devices placed along the path taken by packets that constitute the TCP flow. Some examples of the kinds of processing currently performed on TCP flow between devices include TCP acceleration, acceleration of an application-layer software application using TCP, and intrusion detection.
However, one common requirement for effectively performing intermediate processing is to have all packets in each direction of the TCP flow pass through a single intermediate device that performs the processing. In networks with multiple paths, sometimes called asymmetrically routed networks, it is usually not possible to meet this requirement. In an asymmetrically routed network, a packet forwarded in a first direction between two communicating devices may traverse a different path from a packet forwarded between the devices in the opposite direction. That is, for the same TCP flow, packets from device A to device B may take one path through the network, but packets from device B to device A may take a different path. In this situation it is difficult to make use of a single intermediate device to perform processing on the TCP flow unless the intermediate device can be located before the split in the network routes.